A variety of implantable medical devices (IMDs) for delivering a therapy or monitoring a physiologic condition of a patient have been clinically implanted or proposed for clinical implantation in patients. Some implantable medical devices may employ one or more elongated electrical leads and/or sensors. Such implantable medical devices may deliver therapy or monitor the heart, muscle, nerve, brain, stomach or other organs. In some cases, implantable medical devices deliver electrical stimulation therapy and/or monitor physiological signals via one or more electrodes or sensor elements, which may be included as part of one or more elongated implantable medical leads. Implantable medical leads may be configured to allow electrodes or sensors to be positioned at desired locations for delivery of stimulation or sensing. For example, electrodes or sensors may be located at a distal portion of the lead. A proximal portion of the lead may be coupled to an implantable medical device housing, which may contain electronic circuitry such as stimulation generation and/or sensing circuitry.
An implantable medical device may include a master device that communicates with a plurality of slave devices, such as sensor modules, in order to monitor various conditions including, for example, cardiac electrical activity, blood pressure, blood perfusion, and blood oxygen content. Both the master device and the slave devices may be implanted within the body. A bus may be used to provide communication between the master device and the slave devices. However, a large number of electrically conductive wires on the bus may cause interference and disturbance to the body of the patient. In addition, an implantable medical device may include an internal power source, usually in the form of a battery, which has a limited amount of available power. Because replacement of the implantable medical device requires surgery to the patient, conservation of power is an important consideration. Implantable medical devices often deliver life-supporting therapy in the form of electrical stimulation to the patient, which requires a reliable communication protocol between the master device and the implantable sensors.